Measuring instrument.



G. E. HOLMES.

MEASURING INSTRUMENT.

APPLICATION FILED JULY 1a, 1908.

994,923, Patented June 13, 1911.

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Witnesses: Inventor:

M Charles E. Holmes. m bg G. E. HOLMES. MEASURING INSTRUMENT.

APPLICATION FILED JULY 18, 1908.

Patented June 13, 1911.

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Inventor Charles E. -jo |mes;

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- Witnesses:

Q, W1 w w UNITED STATES PATENT OFFICE.

CHARLES E. HOLMES, 0F LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MEASURING INSTRUMENT.

Specification of Letters Patent. Patented J 1111 13, 1911.

Application filed July 18, 1908. Serial No. 444,217.

To all whom it may concern:

Be it known that 1, CHARLES E. HOLMES, a citizen of the United States, residing at Lynn, in the count-y of Essex and State of Massachusetts, have invented certain new and useful Improvements in Measuring Instruments, of which the following is a specification.

My invention .relates to measuring instruments and more particularly to instruments having a moving coil and a permanent mag- 'net wlth an annular air gap through wlnch the coil moves.

Measuring instruments having a permanent magnet for producing the field should have a very narrow air gap and a very light moving coil. ment the magnet has pole pieces with circu lar faces, and a cylindrical core is fixed concentric with the pole pieces, leaving a very narrow annular air gap between the faces of the pole pieces and the surface of the core, while a light moving coil is made by windin fine wires on a rectangular framework 0 very thin aluminum or other.nonmagnetic material mounted on pivots concentric with the annular air gap. The coil must be thin enough to swing freely through the air gap and must be made comparatively wide in order to give the necessary torque, so that the frame upon which the coil is wound must be made in the shape of a cylinder. 'slightly larger than the core and mounted concentric therewith. Since the clearance between the core and the frame is very slight, the distance between the edges of the framework is often less than the diameter of the core, so various expedients, such as cutting a groove in the core, must be resorted to in order to slip the framework over the core and bring it into a posi- 'tion where it can swing freely in the annular air gap, The coil frame must be shaped about a cylindrical former .slightly larger than the core and made collapsible to permit removal of the former from the interior of the coil frame. Difiiculties are encountered in maintaining the cylindrical core exactly concentric with the pole pieces, particularly wherethe core and coil are removable from between the pole pieces, and also in preventing injury to the coil when the moving system isremoved, while in instruments in In one type of instru-.

which the pole pieces are independent and are mounted on opposite ends of a comparatively large magnet any distortion or change of shape in the magnet causes relative movement of the pole pieces and distorts the air The object of my invention is to provide a measuring instrument with an easily constructed moving coil which, conforming to the shape of the core and swinging about it freely with a very slight clearance. can be easily slipped over a plain cylindrical core to swing concentric therewith: which is so mounted that its weight partially counterbalances the weight of the pointer, thereby eliminating heavy counter weights and rendering the moving system as a whole lighter than those heretofore used, which has the pole pieces held in rigid relation to each other, and fitted to the magnet by machined surfaces, in which the core is accurately .placed in proper relation to the pole pieces without necessity of changes and adj astments by skilled labor, in, which themoviug coil cannot be damaged by striking against the pole pieces during removal and replacement of the moving system, and in which various details of construction are improved. My invention will best be understood in connection with the accompanying drawings, which are merely illustrative of one embodiment thereof, and in ivhich- Figure 1 is a plan view of an instrument embodying my invention; Fig. 2 is an en larged view showing the relation of the moving system to the pole pieces and the core; Fig. 3 is a view, partly in section, of the' moving coil showing the location of the pivotsathereon; Fig. 4: is a view in perspective of the core and the moving coil removed from' the instrument; Fig. 5 is a cross-section of the. pole pieces, core and moving coil, showing their relative positions; while Fig. 6 shows a cap or core support; Fig. 7 the core; Fig. 8 the radial projections or ribs on the core with the screws for fastening the core in position between the pole pieces; Flg. 9 the cross-piece car- 1 drawings comprises "a base 1 of the usue l for-m having clamps 2 for the purpose of l rmly holdingthe permanent magnet 3 in it: properf position on the base. This inagrut is provided with detachable annular pole pieces 4, shown in Figs. '5 and 10, which one role a cylindrical core '5 concentric with the concave faces of-the pole pieces and of such a diam? eter that a narrow annular ai r gap is left between the surface of the core and the faces of the pole pieces. The :noving coil 6 is mounted concentric with the core and its sides move through the annular air gap bctween the pole pieces and the :ore.

The form of the moving cc i1 6 of the instrunicnt is best shown in Figs. 2 and 3.

The framework or shell 7 with-flanges 8 acts as a' support for the wiresand also as a damping frame to render the instrument deadbeat, and is made of: aluminum or other suitable metal stamped into the shape shown in Fig. 2, with the aides of the shell the annular air gap made in the form- 0 porti nus of a cylinder slightly larger than that are 5, these portions being included between a plane A B slightly to one side of the 4 enter of the cylinder and a plane C D parallel to A B and.

some distance on the otl er side of the center. The sides of the sh ll are therefore unsymmetrical with refere .ice to a plane passing through the two sides and the axis of the cylinder of which hey are a part. The width ,of the opening in the frame 7 along the plane A B is substantially the same as the diameter of the sore, while the Width of the opening on the plane (I D is very considerably less than the diameter of the core,-

while the greatest distance across the shell is along a diameter very close to the plane A B but between that plane and the plane C D. If the air gap is suficiently great the sides of the shell need not be truly cylindrical so long as the coil swings freely, but

it is desirableto make the air gap narrowand'the sides of uhe shell cylindrical to obtain proper clearance. I

After the shell is. formed, the wires 9 are wound thereon 'indthen the pivots 10 with bases 11 are sesured tot-he coil or in any suitable wayat the-extremities of that diameter which passes through both sides of the coil andis paralleljto the plane A B.

a The current is led to the coil from controlling springs to which theendspf the wires 9 are connected in the usual manner. 'Since the pivots as shown in Fig. 3 areunounted on the diameter of the coil very near one side thereof, the greater portion of; the coil is on one side of the diaincterzv joining' the pivots. A hub 12 for thepointer attached to one of the" pivots carries, anjndex 13 w "h swings over the scale ltandexten ds in such a direction that its weight s countersee-gees balanced by the weight of that portion of the coil on one side of the pivots. If for any reason all of the weight of the pointer is not counterbalanced. by the coil a very slight counterweight 15 is attached to the hub 12 directly opposite the index 1.3. r

A moving coil constructed in accordance with my invention will swing in a very narrow air gap, and no difficulties are encountered in placing the coil over the core 6, since as shown in Figs. 2 and "5 the opening of the frame on the plane A B is large enough to permit the frame to slip over the core thereby bringing the pivots into alinement with the axis of the core and positioning the coil so that it will swing around the core with proper clearance.

The pole pieces l are held in fixed and unchangeable relation to each. other by means of space blocks 16, of some suitable non magnetic material, such as brass, welded, soldered, or otherwise fastened to the ends of the pole pieces to make the two pole pieces and the space blocks into substantially an integral block of metal which can be machined into'any desired shape and will retain that shape indefinitely. The preferred form is'that shown in the drawings, in which the pole pieces, ea'ch forming approximately a semi-circle, confront each other to leave a cylindrical opening between them and have their adjacent ends secured to the space blocks 16. The entire pole-piece structure may be turned and bored out truly cylindrical like a single block of metal, and

it is necessary that it be mounted exactly concentric with the pole pieces 4, in order to secure a uniform annular air gap. This result is secured by providing the core with radial projections 17 and 18made substantially integral with the core by being held in grooves 19 and 20 by screw s or' other suit-' able fastening means and provided with shoulders 21 and 22, at right angles to the axis of the core 5. A ring-shaped cap or core support 23 is attached, to the shoulders 21 and 22, and carries in a bridge 24a bearing. 24 for the upperpivot of the coil,

while to the lower ends of the projections 1? and 18 a crossbar 25 issecuredto carry the lower bearing 26 for the lower pivjotf oi the coil. The cap and. bridge are of one piece of metal, and form a very rigid support for the bearing 24, which is therefore held in unchangeable relation to'the core on .account of themetal to metal contact of the cap and its shoulders 21 and 22.

The outer surfaces of the radial projections are shaped to conform to the face of the pole pieces 4, and in the specific form. shown in the drawings aremade cylindrical vto fit snugly against the inner circular wall or pole faces of the pole-piece structure. The distance from the surface of the core to the outer surface of the projections dctermines the width of the air gap between the pole pieces and the core, and the projections are preferably turned in a lathe,

with the axis of the core as a center, to form a cylindrical plug which will fit snugly into the cylindrical opening formed by the pole pieces 4: and the space blocks 16. Since the core is truly concentriowith the cylindrical surfaces of the projections 17 and 18, it is necessarily truly' concentric with the pole pieces when the parts ,are assembled and the core is positioned by the reject-ions en gaging the faces of the pole pleces 4 and the inner surfaces of the space blocks. The core is therefore positioned concentric with the pole pieces by the project-ions 17 and 18 and is held in the proper longitudinal positionbetween the pole pieces bythe shoulders 21 and 22' which engage the edge of the pole or of pole-piece structure. All the parts which determine the size of the air gap and the location .of the core are finished by machine tools and .it is therefore possible to put the magnetic system together and secure the exact relation of parts desired without the. system within such limits that the coil -cannot strike the pole pieces. .In many instruments heretofore used great care is necessary to prevent striking the coil against the pole piece during the removal or insertion of themoving system, and I desire to be understood as considering to be within the scope of my invention any construction ofparts which positively guides or rcstrains the moving system during its removal or insertion to such an extent that contact of the coil and pole pieces is prevented.-

The parts when in the assembled position are rigidly held in proper relation by means of threaded pins Q'Ifwhichipass through the holes 28 in the space blocks, through holes 29 mths projection 17 and the core,through smaller holes 30 in the projection 18 into threaded holes in the space block, thereby exerting a radial thrust on the core and locking the core and the pole-piece structure together. Removal of the pins permits end wise removal of the core and attached parts, while in reassembling no special care is re .quired-as the pins merely fasten the core in place and hold it in'fixed and immovable relation to the pole pieces.

It will be noted that the projection 18 is wide enough to span the space block 16 and engage directly with the two adjacent pole faces, thereby accurately positioning the core with relationto the pole faces. As shown in Fig. 8, the pins 27 have shoulders on them which engage the projection.18 and clamp it rigidly in engagement with the pole faces to hold the moving system in position. The pins 27 therefore have nothing to do with positioning the core, but merely act as hold ing means for maintaining the projection 18 in fixed relation to the pole faces.

My invention may be embodied in many other forms than that shown and described,

appended claims all changes and modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. In a measuring instrument, the combination with a magnet having curved confronting pole pieces with their adjacent ends united to non-magnetic space blocks to form an integral structure with a cylindrical opening between the pole pieces, of a cylindrical coreahaving non-magnetic radial projections of equal length to engage the walls of said opening and thereby position the core concentric with said pole pieces, and means for clamping one of said projections to the walls of said opening. y

2. In a measuring instrument, the combiof a magnetic system, of a moving coil having the form of a section included between and on opposite sides of the axis of a hollow cylinder larger than said core.

3. In a measuring instrument, the combination with a magnetic system having an annular air gap, of a moving coil forming a part of the surface of a cylinder included between parallel planes at unequal distances from and on opposite sides of a diameter, and pivots mounted in the axis of said cylinen i 4:. In a mcasuring instrument, the combiand I do not wish to be restricted to the exact form shown but intend to cover by the nation with a cylindrical coreforming part.

parallel planes at different distances from nation with a cylindrical core, of a moving In Witness whereof, I have hereunto set coil shaped as a longitudinal section of a my hand this 16th day of July, 1908. cylinder of greater diameter than the core, said section including the axis of the cylin- GHARLLS HOLMES 5. der and being unsymmetrical with reference 'Witnesses: 'to said axis, and pivots mounted on the coil JOHN A. MGMANUS, J12,

' in the axis of the cylinder. CHARLES A. BARNARD. 

